People exposed to pesticides for many years may be at greater risk of dementia. The warning comes from a study of 614 French vineyard workers whose mental functioning was tested over a period of up to six years between 1997 and 2003.

Pesticides are suspected of causing a range of conditions from autism to cancer, but epidemiological evidence of their long-term effects has been been lacking. The new study is claimed to be the first to provide prospective data on potential neurological damage.

All the workers were aged 45 to 55 and had spent at least two decades working either directly with pesticides (mixing or spraying them), or with treated plants, or in buildings nearby. They were given nine "neurobehavioural" tests designed to measure memory and recall, language retrieval and verbal skills, and reaction times.

The results showed that those who had mixed or sprayed the pesticides were five times more likely to be among the lowest scorers and twice as likely to deteriorate.

The researchers, from the Institute of Public Health in Bordeaux, France, say the "mild impairment" observed raises the question of a "possible evolution towards neurodegenerative diseases such as Alzheimer's disease".

The findings relate to historical exposure, mainly in the 1970s and 1980s, and although the same broad categories of pesticide were used in the UK, their relevance to exposure today is uncertain.

British experts questioned the significance of the study, noting the small number of participants, the tenuous nature of the link with dementia and the fact that other factors could explain the results.

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